a) Field of the Invention
The present invention relates to a method of manufacturing a field emission element, and more particularly to a method of manufacturing a field emission element having an emitter tip with a small radius of curvature and a small apex angle.
b) Description of the Related Art
A field emission element emits electrons from a sharp tip of an emitter by utilizing electric field concentration. For example, a flat panel display can be structured by using a field emitter array (FEA) having a number of emitters disposed on the array. Each emitter controls the luminance of a corresponding pixel of the display.
FIGS. 19A and 19B illustrate conventional manufacture methods of a field emission element.
As shown in FIG. 19A, on a substrate 101 having a recess with a vertical side wall, a sacrificial film 103 is deposited by a deposition method having good step coverage. The upper surface of the sacrificial film 103 has a tapered portion at the recess, which portion broadens its area toward the upper surface. An emitter electrode (cathode) film 105 is formed by using this sacrificial film 103 as a mold (cusp). Thereafter, the substrate 101 and sacrificial film 103 under the emitter electrode film are removed to form an emitter electrode 105 having a sharp tip A. The radius of curvature of the tip A of the emitter electrode 105 depends upon the shape of the recess and the deposition conditions of the sacrificial film. If the radius of curvature is large, an electric field is hard to concentrate and the electrical performance is not good.
As shown in FIG. 19B, if a sacrificial film 103 is deposited thick on a substrate 101 having a recess, two parts in cross section of the sacrificial film 103 at the recess become partially in unison so that an emitter electrode 105 having a relatively small apex angle of the emitter tip can be formed.
With this method, however, it is necessary to deposit the sacrificial film thick so that the tip of the emitter electrode 105 is formed at a higher position remote from the bottom of the recess in the substrate 101. If a field emission element has a gate electrode in addition to an emitter electrode, this gate electrode is generally formed near at the boundary between the substrate 101 and the sacrificial film 103, although not shown in FIG. 1913. With the method illustrated in FIG. 19B, the emitter electrode 105 is formed remotely from the gate electrode so that a high drive voltage of the field emission element is required and the electrical performance is lowered.
As described above, a large radius of curvature of the emitter electrode tip makes an electric field hard to concentrate, lowering the performance of the field emission element. A relative position of the emitter and gate electrodes greatly influences the performance of the field emission element.